Choosing a camera for a particular application typically involves a combination of selecting and compromising desirable traits. A wide field-of-view (FOV) can improve image context, can broaden information content, and, when stabilizing video or emphasizing a particular area of interest, can allow flexibility for cropping. Higher spatial resolution images can reduce pixelation and resolve additional detail for a particular field of view. Lower-noise images can provide a higher-fidelity representation of the scene. And in video systems where control is involved, higher frame rates and lower latency can improve system controllability in closed-loop control systems and can improve response time in other situations.
Although most camera systems detect visible light, other detector wavelengths, especially near IR, SWIR, MWIR, and LWIR also provide useful information. Although visible camera systems are most common, thermal-imaging camera systems (MWIR and LWIR) have significant potential for use in new applications. Small mobile electronic devices, such as handheld instruments, cell phones, and unmanned aircraft, can all benefit from thermal imaging, provided they are available at acceptably small size, low weight, low power, low cost, and with acceptable image quality.
For each desirable camera trait, there may be a number of negative-impact tradeoffs or limitations to be considered or managed. For example, focal plane array manufacturers have migrated to higher pixel counts to improve image quality, but this typically increases the size, weight, power, and cost, limiting their availability for these new markets. Camera size and weight increase dramatically with pixel count since size and weight generally increases to the third power of pixel size, AFOV, and inverse IFOV.Size & Weight ∝ [pixel size*AFOV/IFOV]^3   [Eq. 1]
Widening the angular field-of-view (AFOV) can decrease spatial resolution (image detail) and increase lens and system size, weight, and complexity. In order to maintain spatial resolution (e.g., instantaneous field of view (IFOV)) as the AFOV is increased, the number of pixels in the detector array must be increased which typically increases detector and system size, weight, power, and cost. There are also state-of-the-art technological and commercial/manufacturing limitations in regard to maximum detector size, total detector pixel count, and pixel pitch.
Efforts have been made in the past to stitch two or more images together to form a composite image having a large field of view than the angular field of view of the camera. Conventional techniques involve locating a common feature in a first and second image using image analysis, and then optically aligning and overlaying the first and second images. Identifying a common feature in multiple images, optically aligning the multiple images, and overlaying the multiple images is a computationally intensive process.
Higher spatial resolution images imply narrower per-pixel IFOV and may increase lens-design complexity, size, weight, and manufacturing costs. This will also typically increase camera system size, weight, power, and cost. Image noise may also be increased. There are also physics limits dependent on the wavelength of the imaged light where the effective spatial resolution becomes diffraction limited.
Generating uniform lower-noise images may increase camera system size, weight, power, and cost or may reduce spatial resolution and/or field of view. In addition, lower-noise high-fidelity images may require increased exposure time or otherwise reduce image throughput due to periodic or as-needed collection of sensor-mapping data for non-uniformity correction (NUC). For thermal cameras, this might involve mechanical shutters or a scene-based non-uniformity correction (SB-NUC). Mechanical shutters increase the mechanical complexity and typically decrease reliability. A SB-NUC does not require additional mechanical systems, but may dramatically increase processing complexity, power dissipation, and impose operational constraints.
Higher frame rates and low latency, dependent on how this is accomplished, may increase cost, reduce spatial resolution, or increase noise. Size, weight, power, and cost may increase with the required increases in processing and bandwidth. For thermal cameras, there may be export controls, arms regulations, or other regulatory restrictions based on the maximum frame rate (and resolution). Performance of thermal imaging cameras may also be limited by the detector's thermal time constant. Increasing the frame rate will also increase the power requirements and may increase self-heating. Self-heating can degrade the image quality or, if active cooling is needed, can dramatically increase power and weight requirements.
What is desired, however, is to be able to improve a camera system's field of view, image resolution, image uniformity, frame rate, without increasing the camera system's size, weight and power requirement. It is to such an improved camera system that the present disclosure is directed.